Wiper plugs are used to displace cement from a tubular string that has just had cement pumped through its lower end and into a surrounding annular space to seal it. Typically, a cement shoe keeps the pumped cement from coming back from the annulus into the string through which it was delivered. Some systems deliver a wiper plug as a spacer before the cement is delivered and another wiper to go behind the cement. Wiper plugs generally comprise of a series of cone shaped structures parallel to each other generally made of a resilient material. They are held above a wellhead in an enclosure called a lubricator which in essence is a long tubular with valves near opposed ends. The lubricator allows the well to be isolated to load the wiper plug or plugs and then the loading valve to be closed and the drop valve to be opened to release the wiper plug into the wellbore string. The string generally has a sub for catching the wiper plug called a landing collar.
Some strings have off center components such as a side pocket mandrel. When such devices are in the wellbore the wiper plugs are made longer than normal so that they can straddle the side opening with wiper assemblies so that their downward momentum is not lost at the side opening. Typically the side opening is longer than the length of the wipers on a typical wiper plug. The solution to this problem in the past has been to make significantly longer wiper plugs with two spaced apart assemblies so that as the lower wiper assembly aligns with the opening to the side pocket, the upper wiper assembly is still above and can be driven down with pressure from the surface. Subsequently, when the upper wiper assembly is at the entrance to the side pocket, the lower wiper assembly has cleared the entrance to the side pocket and pressure from the well surface can act on the lower wiper assembly to continue the movement of the wiper plug to the landing collar.
Providing such extended wiper plug assemblies has resulted in having to make the lubricator longer to accommodate them. This has created problems in certain installations because of space available has been limited and access to the top of longer lubricators has also been limited. Further there is the issue of providing adequate bracing to a very long and slender structure that is stood on end in normal service.
The present invention addresses this issue by providing a telescoping wiper plug that can be installed in a lubricator of a reasonable length and when launched is able to extend in length so that it can be properly propelled beyond offsets in a string such as a side pocket mandrel. These and other aspects of the present invention will be more readily apparent to those skilled in the art from a review of the description of the preferred embodiment which appears below with the associated drawings while recognizing that the scope of the invention is determined by the claims.